1. Field of the Invention
This invention relates generally to disconnect tools, and more particularly to a disconnect tool incorporating a coupling for connecting to tool, tubing, or pipe, and a disconnect mechanism.
2. Description of the Related Art
Disconnect tools have long been known in the field of well drilling and servicing equipment. A disconnect tool is employed in a working string or bottom hole assembly ("BHA") to provide the capability of disconnecting the coiled tubing or drill pipe upstream from the working string or BHA. The disconnect tool is activated in situations where the working string has become stuck to such a degree that it cannot be readily dislodged from the wellbore either through upward thrust on the drill pipe or coiled tubing or via jarring forces imparted by a drilling jar, alone, or in combination with an accelerator incorporated into the working string. After the disconnect tool has been actuated and the removeable portion of the tool and upstream portion of the drill pipe or coiled tubing have been withdrawn from the wellbore, a fishing tool is normally inserted in the wellbore to engage and dislodge the stuck working string. Although the problem of stuck tools is present in both coiled tubing and conventional drill pipe operations, the requirement for a reliable disconnect capability is often more important in coiled tubing operations, since coiled tubing has a limited capacity to apply upward thrust on a stuck tool.
Most conventional disconnect tools consist of a tubular housing subdivided into two sections joined together at a joint that may be selectively decoupled to enable the two sections to be separated so that the length of tubing or string above one of the sections may be removed from the wellbore along with one of the sections. The upstream section of the housing ordinarily includes some type of coupling for connecting the disconnect tool to the drill pipe, coiled tubing, or wireline, as the case may be. The lower section of the housing also includes a coupling of one sort or another for connecting the disconnect tool to other components in the string, such as additional drill pipe or other tools. In the case of drill pipe, this lower connection is commonly a pin or box connection.
The tool-to-coiled tubing coupling mechanism in many conventional disconnect tools consists of a hydraulically actuated mandrel which is movable longitudinally to set or wedge sets of cooperating teeth together to engage the exterior of the end of a piece of coiled tubing. These types of mechanisms may loosen over time as a result of cyclic stresses that are commonly applied to a working string in the downhole environment. As the coupling loosens, there is the potential for the coiled tubing to disconnect from the disconnect tool. The result is an unanticipated and potentially costly fishing operation. In addition, hydraulically actuated coupling mechanisms tend to be quite lengthy. The length of a particular disconnect tool is ordinarily not a significant issue in drilling operations where regular threaded drill pipe is utilized. However, in coiled tubing applications it is desirable that the length of all the tools in a particular drill string be no longer than the length of the lubricator of the particular coiled tubing injector. Thus, it is desirable that the disconnect tool be economical in length to enable the operator to place as many different types of tools in the working string as possible while still keeping the overall length of the working string less than the length of the lubricator.
Another type of conventional coupling mechanism commonly employed in disconnect tools incorporates a sliding collar or a set of grub screws. Like the aforementioned hydraulically actuated mandrel mechanism, both the sliding collar and grub screw based mechanisms are subject to inadvertent disconnection, due to unavoidable play in the engagement between cooperating members or to the mechanism employed to prevent relative axial movement of the members. Undesirable length is also a drawback.
The disconnect mechanisms in most conventional disconnect tools may be loosely grouped into three basic categorizes: pull or thrust actuated; pressure actuated; and electrically actuated. Thrust actuated systems contain some type of mechanism which retards the axial movement of a mandrel or sleeve that is concentrically disposed in the housing. In most conventional thrust activated systems, the mechanism for resisting relative axial movement consists of sets of shear pins or a collet that are designed to fracture or collapse when a preselected axial thrust is applied to the working string from the surface. In another type of system used primarily on coiled tubing, the lower end of the coiled tubing is fluted against an inwardly chamfered surface on the housing. When the axial upward thrust applied to the working string exceeds a preselected limit, the fluted portion of the coiled tubing yields and releases from the disconnect tool.
Thrust activated disconnect tools present several disadvantages. In systems where the entire weight of the working string disposed below the disconnect tool is supported by the shear pins or collet, the axial jarring loads that are commonly imparted on the working string during operations may weaken the shear pins or collet so that the required upward axial thrust required to fail the shear pins or collapse the collet, as the case may be, is reduced below the anticipated level. As a consequence, the disconnect tool may be inadvertently triggered by applying an upward thrust on the working string for operational reasons other than tripping the disconnect tool. In addition, a given upward axial thrust load may not be fully transmitted to the disconnect tool. This circumstance may arise in wellbores with mechanical or formation-based obstructions that engage portions of the working string upstream from the disconnect tool. The problem may be compounded in highly deviated wells where the coiled tubing typically bottoms out against the sidewalls of the wellbore in the vicinity, and downstream of the bend in the wellbore. As a consequence, a greater than anticipated upward axial thrust must be applied to the working string from the surface in order to trigger the disconnect mechanism. This may be problematic in circumstances where the amount of upward axial thrust required to overcome the obstructions in the wellbore and provide a sufficient triggering load on the disconnect mechanism exceeds the yield or fracture strength of the tubing or any other components upstream from the disconnect tool.
In contrast to thrust activated disconnect mechanisms, pressure activated disconnect mechanisms operate in response to an increase in the pressure of the working fluid inside the working string. These types of disconnect mechanisms commonly incorporate a moving piston which moves axially in response to an increase in pressure above a preselected level to release or otherwise trigger a mechanical mechanism, such as a collet, or one or more radially movable dogs. In some conventional pressure actuated disconnect mechanisms the requisite increase in working fluid pressure must be supplied from the surface. Robust and costly high pressure pumping equipment must normally accompany the use of such disconnect mechanisms. In other types of pressure activated disconnect mechanisms, the requisite build-up of working fluid pressure inside of the disconnect tool is accomplished by introducing an obstruction to the flow of working fluid through the disconnect tool downstream from the tripping mechanism. This is typically accomplished by dropping a scaling ball into the drill pipe or coiled tubing from the surface. The ball travels down through the tubing and seats on a shoulder in the disconnect tool downstream from the tripping mechanism, thereby closing off the flow path and enabling the pressure of the working fluid to build to the requisite level. Proper operation of pressure activated disconnect mechanisms places heavy demands upon the seals within such tools. If one or more of the seals in a given pressure activated disconnect tool fails, the pressurized working fluid inside the disconnect tool may vent into the well annulus without tripping the mechanism.
In addition, pressure activated disconnect mechanisms are subject to inadvertent actuation as a result of unanticipated pressure increases inside the disconnect tool caused by obstructions in the flow path of the working fluid downstream from the disconnect tool. As an example, an obstruction in the disconnect tool itself may cause the same effect as a scaling ball. The unanticipated increase in working fluid pressure may not be sensed at the surface in time to bleed pressure from the surface and avoid an inadvertent disconnection. Finally, in pressure activated disconnect systems employing a scaling ball, obstructions in the drill pipe, coiled tubing, or other components may prevent the scaling ball from actually reaching the proper position in the disconnect tool.
Electrically actuated disconnect mechanisms normally employ an electric motor to release a collet or set of dogs. The difficulty associated with such systems is that jarring forces and manufacturing irregularities may produce misalignment of the moving parts. As a result, the moving components may not readily move when the motor is actuated, leading to a potential locked rotor current condition that may quickly fail the motor. In addition, power loss from the surface may cripple this type of tool.
A disadvantage common to most conventional disconnect tools is the inability to reconnect following a deliberate or inadvertent disconnect.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.